A half-bridge LLC resonant converter with loose-coupling transformer and transition capacitor

In this paper, a half-bridge LLC resonant converter with a loose-coupling transformer and a transition capacitor is analyzed and implemented. The LLC resonant tank is comprised with a loose-coupling transformer and a series-resonant capacitor. For transiting the resonant current of the switching transistors and improving the zero-current turn off of the rectifying diodes, a small transition capacitor is added and paralleled to the switching transistors. To verify the analysis of the switching circuit, circuit simulation is executed. And, to demonstrate the design of the LLC converter, a 200W prototype is built and tested. The DC input and output ratings of the converter are 400V and 12V, respectively. The experimental results coincide with the design and prediction.